Nitrogen Rich Materials: Salts of N,N�-Bistetrazolatohydrazine

Anton Hammerla, Gerhard Hollb, Manfred Kaiserb, Thomas M. Klapötkea,*, and Holger Piotrowskia

a München, Department of Chemistry, Ludwig-Maximilians-University of Munichb Swisttal, Wehrwissenschaftliches Institut für Werk-, Explosiv- und Betriebsstoffe

Received April, 24th, 2003.

Dedicated to Professor Bernt Krebs on the Occasion of his 65th Birthday

Abstract. Solutions of N,N�-azobistetrazolate salts in anhydrous hy-drazine were reduced to salts of N,N�-bistetrazolatohydrazine. Seve-ral salts of this highly energetic, nitrogen rich anion were preparedthis way and characterized by elemental analysis, vibrational (IR,Raman) and multinuclear NMR spectroscopy (1H, 13C, 14N). The

Stickstoffreiche Verbindungen: Salze von N,N�-Bistetrazolatohydrazin

Inhaltsübersicht. Lösungen von N,N�-Azobistetrazolatsalzen in Hy-drazin wurden innerhalb einiger Tage zu N,N�-Bistetrazolatohydra-zin reduziert. Auf diese Weise wurden mehrere Salze dieses hoch-energetischen, stickstoffreichen Anions hergestellt und durch

Introduction

In recent years nitrogen rich materials like 3,3�-azobis(6-amino-1,2,4,5-tetrazine) [1] and salts of the azobistetrazo-late ion were investigated [2]. The explosive energy of thesecompounds derives from their high positive heat of forma-tion. These materials include huge amounts of nitrogen andare used as propellants and gas generators. Hydrazine, itssalts and its derivatives are important endothermic buildingblocks for this substance class. The explosion of hydrazi-nium compounds results in the environmentally safe gasesnitrogen and hydrogen as well as small amounts of ammo-nia. N,N�-Bistetrazolatohydrazine salts were first preparedby Thiele by reduction of N,N�-azobistetrazolates with mag-nesium [3]. Several aqueous salts were synthesized withthis method and their thermal decomposition was analyzedwith TG and DSC [4]. We have investigated hydraziniumsalts of different nitrogen rich anions (including azide andN,N�-azobistetrazolate) [5]. We found that a solution of aN,N�-azobis-tetrazolate salt in anhydrous hydrazine is redu-ced to a salt of N,N�-bistetrazolatohydrazine [6]. Here wepresent our studies of several N,N�-bistetrazolatohydrazinesalts and the crystal structures of barium N,N�-bistetra-zolatohydrazine·trihydrazine and hydrazinium N,N�-bis-tetrazolatohydrazine·hydrazine.

* Prof. Dr. Thomas M. KlapötkeDepartment Chemie, Ludwig-Maximilians-UniversitätButenandtstr. 5�13 (Haus D)D-81377 Münchene-mail: thomas.m.klapoetke@cup.uni-muenchen.de

Z. Anorg. Allg. Chem. 2003, 629, 2117�2121 DOI: 10.1002/zaac.200300151 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 2117

crystal structure of the barium and hydrazinium salt were deter-mined.

Keywords: High energy materials; Hydrazine; Nitrogen rich com-pounds

Elementaranalyse, IR-, Raman- und NMR-Spektroskopie charak-terisiert. Die Kristallstrukturen von Barium-N,N�-bistetrazolatohy-drazin und Hydrazinium-N,N�-bistetrazolatohydrazin wurden be-stimmt.

Results and Discussion

The N,N�-bistetrazolatohydrazine anion was prepared fromthe reduction of N,N�-azobistetrazolate in anhydrous hydra-zine. The reduction time is dependant on the cation, beingfastest with barium (1). Here the reaction was finished inthe course of a day. For lithium (2), sodium (3) and hydrazi-nium (4) the reaction times were between one week and onemonth. A faster synthesis of the hydrazinium salt 4 is possi-ble by the reaction of barium N,N�-bistetrazolatohydrazine(1) with hydrazinium sulphate. All salts are colorless solidsthat include different amounts of hydrazine molecules coor-dinated in the crystal. If air is introduced to a solution ofa N,N�-bistetrazolatohydrazine 4 in hydrazine the anion israpidly oxidized back to the yellow N,N�-azobistetrazolate.This oxidation also occurs when the solid compounds areexposed to air, but takes several days.

No single crystals of 2 and 3 could be obtained. The mic-roanalyses for all compounds are not in good agreementwith the calculated values, which often happens for com-pounds with high nitrogen content [1, 6]. Therefore, it wasnot possible to determine the exact amount of coordinatedhydrazine molecules present in 2 and 3.

The 1H NMR spectra of 1�3 shows one signal for allhydrazine hydrogen atoms around δ � 3.3 and at δ � 5.15for 4. The carbon atoms of the N,N�-bistetrazolatohydra-zine ion appear in the 13C NMR spectrum around δ � 166for 1�4. This is at lower field compared to δ � 173 obser-ved for the carbon atoms of N,N�-azobistetrazolate [2]. The14N NMR in [D6]DMSO displays no absorptions for theN,N�-bistetrazolatohydrazine ion. Signals in 14N NMR

A. Hammerl, G. Holl, M. Kaiser, T. M. Klapötke, H. Piotrowski

spectra are often very broad or missing [2]. The hydrazinenitrogen atoms appear around δ � 335 for all compounds.

Crystal structures

The bonding parameters of the N,N�-bistetrazolatohydra-zine anions in 1 and 4 agree with each other (s. figures).The tetrazolate ring bonding parameters are in goodagreement with those observed in N,N�-azobistetrazolatesalts. The N-N bond length for the bridging nitrogen atomshas the expected value of 1.444(7) A for 1 and 1.414(1) Afor 4, corresponding to a N-N single bond.

Figure 1 Coordination of the barium ion of 1 (thermal ellipsoidsrepresent 50 % probability); selected bond lengths/A:Ba-N(1A) 2.958(5), Ba-N(1B) 3.090(5), Ba-N(1C) 3.009(5), Ba-N(2A)ii 3.121(5), Ba-N(2B)iii 2.979(5), Ba-N(2C)iv 2.928(5), Ba-N(32)ii 2.937(5), Ba-N(41) 2.900(5), Ba-N(52)iii 2.887(5), N(1A)-N(2A) 1.440(7), N(1B)-N(2B) 1.451(8), N(1C)-N(2C) 1.453(7); tor-sion angle/°: C(11)-N(11)-N(12)-C(12) 52.8(6). Symmetry: i 1 � x,� y, 2 � z; ii 2 � x, � y, 1 � z; iii 1 � x, � y, 1 � z; iv 1 � x, �

y � 1, 2 � z.

The barium ion of 1 is coordinated to nine nitrogenatoms, forming a tricapped trigonal prism. The Ba-N di-stances are between 2.887(5) and 3.121(5) A. In the threeknown homoleptic barium-amine complexes [7][Ba(NH3)7]2�, [Ba(NH3)8]2� and [Ba(NH3)9]2� the bariumions have coordination spheres in form of a capped trigonalprism, a distorted quadratic antiprism and a distorted tri-capped trigonal prism. Their Ba-N distances vary between2.854(4) and 2.941(7) A, the Ba-N distance ofbariumhydrazinecarboxylate·hydrazine is 2.98(2) A [8]. OneN,N�-bistetrazolatohydrazine ion coordinates to three ba-rium ions. The torsion angle of the N,N�-bistetrazolatohy-drazine unit is 52.8(6). The N,N�-bistetrazolatohydrazine

2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim zaac.wiley-vch.de Z. Anorg. Allg. Chem. 2003, 629, 2117�21212118

Figure 2 Hydrogen bonds between N,N�-bistetrazolatohydrazinemolecules in 1 (thermal ellipsoids represent 50 % probability) for-ming an infinite chain. Hydrogen bonds: N-N distances/AN(11)-H(11)···N(21)i 3.078(7), N(12)-H(12)···N(11)ii 3.190(7); N-Hdistances [A]: N(11)-H(11) 0.89(6), N(12)-H(12) 0.98(7); H···N di-stances [A]: H(11)···N(21)i 2.19(6), H(12)···N(11)ii 2.27(7); N-H···Nangles [°]: N(11)-H(11)···N(21)i 175(5), N(12)-H(12)···N(11)ii

156(6). Symmetry: i 2 � x, 1 � y, 1 � z; ii 1 � x, 1 � y, 1 � z.

molecule is linked with two other N,N�-bistetrazolatohydra-zine molecules via hydrogen bonding. The N-N distancesof the NHN hydrogen bonds exhibit values between3.078(7) and 3.190(7) A. The hydrogen atoms of the hydra-zine molecules are refined from X-ray data with a ridingmodel. Therefore a statement regarding the hydrogen bondsis not reliable. Each N atom of the hydrazine molecules issurrounded by at least 6 other N atoms in a distance bet-ween 3.012(8) and 3.598(8) A. This indicates a complex net-work of hydrogen bonding. The N-N distances are similarwith the N-N distances of the NHN hydrogen bonds inN,N�-azobistetrazolate salts [2] and in hydrazine [9].

The torsion angle of the N,N�-bistetrazolatohydrazineunit in 4 is 85.7(1)° and larger compared to that in 1. In 4opposed to 1 all hydrogen atoms could be located. Everyhydrogen atom of 4 is involved in NHN hydrogen bonding.Each N,N�-bistetrazolatohydrazine ion bonds to six hydra-zinium ions, three hydrazine molecules and two other N,N�-bistetrazolatohydrazine ions. N-N distances between2.852(1) and 3.320(2) A are found for hydrogen bonds bet-ween tetrazolate ions and hydrazinium ions. Hydrogenbonds between hydrazine molecules and hydrazinium ionshave NHN distances between 2.803(1) and 3.412(1) A,which is in good agreement with the hydrogen bonds inhydrazine [9].

Conclusion

Barium N,N�-bistetrazolatohydrazine·trihydrazine (1) is ea-sily prepared by reduction of barium N,N�-azobistetrazolatein anhydrous hydrazine. The reduction works also withother N,N�-azobistetrazolate salts, but takes longer. A fastersynthesis for other salts uses the barium salt 1 and the sul-phate of the desired cation. The synthesis in hydrazine

Nitrogen Rich Materials: Salts of N,N�-Bistetrazolatohydrazine

Figure 3 Hydrogen bonds of the N,N�-bistetrazolatohydrazine ion in 4 (thermal ellipsoids represent 50 % probability). Selected bond lengths/A: N(1A)-N(2A) 1.443(1) , N(1B)-N(2B) 1.444(1), N(1C)-N(2C) 1.444(1); torsion angle/°: C(11)-N(11)-N(12)-C(12) 85.7(1); hydrogenbonds: N-N distances/A: N(11)-H(11)···N(51)iv 2.944(1), N(12)-H(12)···N(41)iii 3.182(2), N(32)···H(11)vii-N(1A)vii 3.088(2),N(52)···H(22A)ii-N(2A)ii 2.854(2), N(42)···H(32A)viii-N(2A)viii 2.880(1), N(42)···H(11B)ii-N(1B)ii 3.264(2), N(32)···H(21B)i-N(1B)i 3.320(2),N(21)···H(12B)ii-N(21)ii 2.851(1), N(11)···H(32B)-N(2B) 3.081(2), N(41)···H(21C)v-N(1C)v 3.361(2), N(31)···H(12C)vi-N(2C)vi 3.192(1),N(31)···H(22C)iii-N(2C)iii 3.235(1). Symmetry: i � x, � y, � z; ii x � 1, y, z; iii � x, 1 � y, 1 � z; iv 1 � x, 1 � y, 1 � z; v x, y � 1, z;vi x � 1, y � 1, z; vii 1 � x, 1 � y, � z; viii � x, 1 � y, � z.

Figure 4 Hydrogen bonds between the hydrazinium ions and thehydrazine molecules in 4 (thermal ellipsoids represent 50 % proba-bility).N-N distances/A: N(1A)-H(21A)···N(1B)i 3.159(2), N(1C)···H(22B)i-N(2B)i 2.752(1); N(2A)-H(12A)···N(2C) 2.803(1); N(1C)-H(11C)···N(1A)iii 3.136(2); N-H distances/A: N(1A)-H(21A)0.92(2), N(2A)-H(12A) 0.95(2), N(2B)-H(22B) 0.99(2), N(1C)-H(11C) 0.86(2);H···N distances [A]: H(21A)···N(1B)i 2.27(2),H(22B)i...N(1C) 1.77(2), H(11C)···N(1A)iii 2.37(2), H(12A)...N(2C)1.87(2); N-H···N angles/°: N(1A)-H(21A)···N(1B)i 162(2), N(2B)i-H(22B)i...N(1C) 172(2), N(1C)-H(11C)···N(1A)iii 150(1), N(2A)-H(12A)···N(2C) 166(2). Symmetry: ix, 1 � y, z; ii x � 1, y, z;iii x � 1, y, z.

yields salts that include different amounts of coordinatedhydrazine molecules which are involved in hydrogenbonding in the crystal. Hydrazinium N,N�-bistetrazolato-hydrazine·hydrazine (4) is a new nitrogen rich compoundthat may be used as a high energy material.

Z. Anorg. Allg. Chem. 2003, 629, 2117�2121 zaac.wiley-vch.de 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 2119

Experimental Section

General Remarks: CAUTION: The reported compounds are explo-sive. Safety equipment like leather gloves, face�shield and ear pro-tection are recommended. All syntheses were carried out usingstandard Schlenk�line techniques under dry argon. Anhydrous hy-drazine was made by manifold distillation of hydrazine hydrate overBariumoxide and was stored under argon. Lithium, sodium andbarium N,N�-azobistetrazolate were prepared according to litera-ture procedures [2]. � NMR: Jeol EX 400, 1H (400.0 MHz), 13C(100.0 MHz): chemical shifts refer to δ TMS � 0.00; 14N(28.6 MHz): shifts refer to CH3NO2. � IR: Nicolet 520 FT-IR (so-lid compounds as KBr-pellets). � Raman: Perkin-Elmer FTIR-2000 spectrometer (Nd-Yag Laser: 1064 nm, Laser power:100 mW). � CHN-analysis: Elementar Vario EL analysator. �

Melting points: Büchi B450.Barium N,N�-bistetrazolatohydrazine trihydrazine (1): 1.28 g(4.2 mmol) Barium N,N�-azobistetrazolate were solved in 15 mL ofanhydrous hydrazine. The color of the solution changed from yel-low to red and a colorless solid started to precipitate. After twohours the red colour had completely disappeared. After filtration acolorless solid was isolated. � Yield: 1.56 g (93 %) � C2H14BaN16

(399.57): C 6.2 (calc. 6.0 ), H 3.4 (3.5), N 54.1 (56.1) %.1H-NMR ([D6]DMSO): δ � 3.21 (s, NH) . � 13C-NMR([D6]DMSO): δ � 167.0. � 14N-NMR ([D6]DMSO): δ � �328. �

IR (cm�1): ν � 3318 m, 2961 s, 2228 w, 1582 m, 1350 w, 1269 m,1098 m, 1016 m, 798 s, 398 w. � Raman (cm�1): ν � 3332 m,3319 m, 3281 m, 3193 w, 1623 w, 1509 w, 1478 w, 1387 w, 1216 m,1196 w, 1156 w, 1108 m, 1048 s, 1002 w, 918 w, 823 w, 766 w, 583 w,449 w, 349 w, 235 w, 220 w, 184 w, 115 m. �

A. Hammerl, G. Holl, M. Kaiser, T. M. Klapötke, H. Piotrowski

Table 1 Bond lengths/A and angles/° for N,N�-bistetrazolatohydra-zine ions.

1 4

N(11)-N(12) 1.444(7) 1.414(1)N(21)-N(31) 1.366(7) 1.358(1)N(22)-N(32) 1.366(7) 1.355(1)N(31)-N(41) 1.314(7) 1.304(1)N(32)-N(42) 1.305(7) 1.299(2)N(41)-N(51) 1.352(7) 1.358(1)N(42)-N(52) 1.371(7) 1.357(1)N(11)-C(11) 1.396(7) 1.391(1)N(12)-C(12) 1.390(7) 1.387(1)N(21)-C(11) 1.322(7) 1.331(1)N(22)-C(12) 1.328(7) 1.328(2)N(51)-C(11) 1.338(7) 1.331(1)N(52)-C(12) 1.336(7) 1.328(1)N(12)-N(11)-C(11) 114.2(4) 116.04(9)N(11)-N(12)-C(12) 114.5(4) 114.02(9)N(21)-N(31)-N(41) 108.8(4) 109.85(8)N(22)-N(32)-N(42) 110.6(4) 109.73(9)N(31)-N(41)-N(51) 110.4(4) 109.48(8)N(32)-N(42)-N(52) 108.7(4) 109.79(8)N(11)-C(11)-N(21) 123.0(5) 124.37(9)N(12)-C(12)-N(22) 124.3(5) 124.2(1)N(11)-C(11)-N(51) 123.3(5) 122.70(9)N(12)-C(12)-N(52) 122.2(5) 122.6(1)N(21)-C(11)-N(51) 113.5(5) 112.83(9)N(22)-C(12)-N(52) 113.2(5) 113.11(9)C(11)-N(21)-N(31) 104.0(4) 103.80(8)C(12)-N(22)-N(32) 103.5(4) 103.76(9)C(11)-N(51)-N(41) 103.3(4) 104.03(8)C(12)-N(52)-N(42) 104.1(4) 103.59(9)

Lithium N,N�-bistetrazolatohydrazine · x hydrazine (2): 0.75 g(4.2 mmol) Lithium N,N�-azobistetrazolate were solved in 10 mL ofanhydrous hydrazine. An orange solution was formed which turnedcolorless within four weeks. Hydrazine was removed in vacuo and0.83 g of a colorless solid was isolated. �1H NMR ([D6]DMSO): δ � 3.40 (s, NH). � 13C NMR([D6]DMSO): δ � 167.6. � 14N-NMR ([D6]DMSO): δ � �335. �

IR (cm�1): ν � 3348 s, 3209 s, 3136 s, 3070 s, 2967 s, 2887 m,2777 w, 1607 s, 1587 s, 1534 s, 1497 s, 1477 m, 1400 s, 1368 w,1262 s, 1236 w, 1157 m, 1139 m, 1096 s, 1036 s, 967 m, 865 w, 803 s,705 w, 687 w, 661 w, 579 m, 477 m, 400 m. � Raman (cm�1): ν �

3328 w, 3278 m, 3216 w, 1616 w, 1542 s, 1380 w, 1364 w, 1225 m,1115 m, 1066 s, 1004 w, 932 w, 888 w, 400 w.Sodium N,N�-bistetrazolatohydrazine · x hydrazine (3): 1.48 g(7.0 mmol) Sodium N,N�-azobistetrazolate were solved in 10 mL ofanhydrous hydrazine. A yellow solution was formed. After two we-eks a colorless solid started precipitating. After four weeks 1.35 gof a colourless solid were filtered off and dried in vacuo. �1H NMR ([D6]DMSO): δ � 3.50 (s, NH). � 13C NMR([D6]DMSO): δ � 166.2. � 14N-NMR ([D6]DMSO): δ � �337. �

IR (cm�1): ν � 3392 s, 3348 s, 3318 s, 3275 s, 3209 s, 3041 m,2967 m, 2909 m, 1673 m, 1631 m, 1597 s, 1573 s, 1510 s, 1479 s,1378 m, 1360 s, 1262 s, 1226 m, 1216 m, 1206 w, 1103 s, 1061 s,1035 s, 1017 s, 1011 s, 962 w, 881 m, 818 s, 805 s, 762 w, 720 w,708 w, 659 w, 613 m, 580 m, 547 w, 487 w, 388 w, 337 w. � Raman(cm�1): ν � 3327 m, 3277 m, 3207 w, 1608 w, 1500 s, 1457 w, 1219 s,

2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim zaac.wiley-vch.de Z. Anorg. Allg. Chem. 2003, 629, 2117�21212120

Table 2 Crystallographic data, and details of data collection andstructural refinement.

1 4

empirical formula C2H14BaN16 C2H16N16

formula weight /g mol�1 399.63 264.31color, habit colorless platelet colorless prismtemperature /K 200(2) 200(2)crystal size /mm 0.22x0.20x0.07 0.50x0.30x0.25crystal system triclinic triclinicspace group P1 P1a /A 7.2357(1) 5.6311(5)b /A 9.2364(1) 8.8659(8)c /A 10.44790(1) 12.701(1)� /° 67.5266(7) 104.40(1)β/° 78.8543(6) 97.52(1)γ/° 80.0431(6) 101.27(1)V /A3 629.27(1) 591.47(9)Z 2 2density (calcd.) /g cm�3 2.109 1.484absorp. coeff. /mm�1 3.177 0.117F(000) 388 280θ range /° 2.13 to 24.00 2.44 to 27.99index range �8 � h � 8 �7 � h � 7

�10 � k � 10 �11 � k � 11�11 � l � 11 �16 � l � 14

reflections collected 9006 5155independent reflections 1973 2630observed reflections(4σ) 1889 2257R (int.) 0.0375 0.0229data/restraints/parameters 1873/0/180 2630/0/228goodness-of-fit F2 1.312 1.062R1, wR2 [I>4σ(I)] 0.0240/0.0611 0.0341/0.0878R1, wR2 (all data) 0.0281/0.0851 0.0403/0.0905largest diff. peak/hole /e/A3 1.211/�1.396 0.280/�0.253

1119 m, 1061 s, 885 w, 835 w, 786 w, 710 w, 585 w, 484 w, 388 w,359 w, 252 w, 232 .Hydrazinium bistetrazolatohydrazine·hydrazine (4): 0.47 g(2.9 mmol) Hydrazinium(�1) sulphate were added to a solutionof 1.15 g (2.9 mmol) barium N,N�-bistetrazolatohydrazine · trihy-drazine (1) in 15 mL of anhydrous hydrazine. A colorless precipi-tate formed and was filtered off after 1 h. Hydrazine was removedfrom the remaining solution in vacuo. The resulting colorless solidwas recrystallized from anhydrous hydrazine. � Yield: 0.59 g(78 %). � m.p.: 150 °C. � C2H16N16 (262.3): C 9.6 (calc. 9.1), H5.1 (6.1), N 81.5 (84.8) %.1H NMR ([D6]DMSO): δ � 5.15 (s, NH). � 13C NMR([D6]DMSO): δ � 165.7. � 14N-NMR ([D6]DMSO): δ � �332. �

IR (cm�1): ν � 3290 s, 3172 s, 3041 s, 2989 s, 2916 s, 2916 s, 2865 s,2762 s, 2771 s, 2623 s, 2169 m, 1617 s, 1571 s, 1555 s, 1529 s, 1470 s,1418 m, 1363 s, 1283 w, 1223 m, 1131 s, 1115 s, 1063 m, 1014 m,1002 w, 961 s, 931 m, 899 w, 818 m, 760 w, 718 w, 608 m, 577 m,449 m. �

X-ray Crystallographic Study:

The single crystals were submerged in dried paraffin oil underanaerobic conditions. A suitable crystal was mounted on a glass

Nitrogen Rich Materials: Salts of N,N�-Bistetrazolatohydrazine

fiber, transferred onto the diffractometer and cooled in the coldgas stream derived from liquid nitrogen. 1 was measured on a No-nius Kappa CCD and 4 on a STOE IPDS diffractometer usinggraphite monochromated Mo-Kα-radiation (λ � 0.71073 A). Allcalculations were performed using SIR97 [12] and SHELXL-97[13].Crystallographic data have been deposited with the CambridgeCrystallographic Data Centre as supplementary publication no.CCDC-207108 (1) and 207107 (4). Copies of the data can be obtai-ned free of charge on application to CCDC, 12 Union Road, Cam-bridge CB2 1EZ, UK [Fax: int. code � 44(1223)336-033; E-mail:deposit@ccdc.cam.ac.uk].

Acknowledgments. Financial support by the Deutsche Forschungs-gemeinschaft (DFG, KL 636/7-1) is gratefully acknowledged.

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